This invention is directed primarily toward providing a latch for securing movable panels in exterior surfaces of aircraft when the load on the exterior surfaces is essentially perpendicular to the surfaces. Such loads are experienced, for example, by strut trailing edge fairings associated with wing mounted engines and by similar structures. The load on access panels on these structures has two major components. First, there is an aerodynamic load resulting from a lower pressure outside the structure than inside the structure. This aerodynamic load is generally directed outwardly and can be quite large even for a small pressure differential since the surface area of the access panel is usually quite large. Second, the access panel is subjected to a seal crush load that is always outwardly directed. The seal crush load results from the panel being pushed down to achieve a faired condition. Since there are usually many inches of seal around the access panel, the total force on the seal is quite large to provide the necessary compression. Current latching mechanisms that are suitable for use in securing external access panels in aircraft are not reliable for securing a panel subjected to such aerodynamic and seal crush loads since these latches react a load applied parallel to the latch mounting surface rather than a load applied essentially perpendicular to the latch mounting surface.
In addition to the outwardly directed load on the panel, there are other problems associated with providing latches for access panels on structures like strut trailing edge fairings. One such problem is a severe limitation on the amount of space available for the latch. Of course, the outer surfaces of the latch must be flush with the outer surfaces of the panel in order to keep the structure faired and maintain the aerodynamic efficiency of the aircraft. Therefore, all of the latch mechanism must be contained within the limited space inside the strut structure. The problem of the limited amount of interior space is aggravated in situations in which there are opposed access panels on either side of a fairly narrow fairing structure.
It is well known that, in order to obtain safe, smooth operation of the latch, it is desirable to tension the latch so that the latch is preloaded even when there is no external load on the panel. Unfortunately, a desirable amount of preload can be sufficient to cause a tendency for the panel to buckle. Therefore, there is a need to provide some means for counteracting this tendency to buckle. Any such means for counteracting buckling must of course fit within the limited space available within the structure.
In many applications, it is important to maintain the preload tension on the latch within a fairly narrow optimum range. In order to accomplish this there must be means for adjusting the tension. Many currently known latching mechanisms do not provide for the adjustment of the preload tension. Of those that do provide for tension adjustment, many require that the latch be opened in order to obtain access to the adjustment means. This requires the latch to be opened and closed a number of times to adjust the tension on a cut-and-try basis. Such a procedure is unreasonably time-consuming and frequently results in a less than optimum adjustment of the tension.
An additional problem associated with latches for securing exterior access panels on aircraft is the danger of the latch not being properly engaged but appearing to be so engaged from the outside. This situation can be highly dangerous for obvious reasons.
The patent literature includes a very large number of patents that disclose latching devices. These patents include German Pat. No. 682,872, Great Britain Pat. No. 594,198, and the following United States Patents:
No. 234,866, granted Nov. 20, 1880, to P. Forg; PA0 No. 671,792, granted Apr. 9, 1901, to E. F. Comber; PA0 No. 2,003,006, granted May 28, 1935, to B. S. Michelson; PA0 No. 2,622,911, granted Dec. 23, 1952, to La Mar S. Cooper; PA0 No. 2,669,477, granted Feb. 16, 1954, to W. R. Jewell; PA0 No. 2,699,962, granted Jan. 18, 1955, to J. E. Hogan et al; PA0 No. 2,712,955, granted July 12, 1955, to W. R. Andrews; PA0 No. 2,750,217, granted June 12, 1956, to E. C. Landholt; PA0 No. 2,904,141, granted Sept. 15, 1959, to B. W. Henrichs; PA0 No. 2,927,812, granted Mar. 8, 1960, to L. D. Smith et al; PA0 No. 2,944,848, granted July 12, 1960, to H. I. Mandolf; PA0 No. 2,951,723, granted Sept. 6, 1960, to B. S. Bernhard; PA0 No. 3,259,411, granted July 5, 1966, to E. G. Griffiths; PA0 No. 3,259,412, granted July 5, 1966, to F. Wheeler; PA0 No. 3,347,578, granted Oct. 17, 1967, to R. W. Sheehan et al; PA0 No. 3,664,696, granted May 23, 1972, to L. R. Poe; PA0 No. 3,712,665, granted Jan. 23, 1973, to N. Klein; PA0 No. 4,053,177, granted Oct. 11, 1977, to Stammreich et al; PA0 No. 4,116,479, granted Sept. 26, 1978, to L. R. Poe; PA0 No. 4,159,137, granted June 26, 1979, to R. D. Richter; PA0 No. 4,183,564, granted Jan. 15, 1980, to L. R. Poe; PA0 No. 4,223,943, granted Sept. 23, 1980, to VanHulle et al; and PA0 No. 4,318,557, granted Mar. 9, 1982, to Bourne et al.
Cooper, Jewell, Landholt, Mandolf, Klein and VanHulle et al each disclose a latching device that is described as being capable of withstanding loads applied normal to the mounting surface or that appears to be designed to withstand such loads. The German and British patents each disclose a latching device that reacts loads at an acute angle to the mounting surface. Andrews, Landholt, Henrichs, Smith et al, Griffiths, Wheeler, Sheehan et al, Klein, Stammreich, et al, Poe U.S. Pat. No. 4,116,479, Richter, Poe U.S. Pat. No. 4,183,564, Bourne et al, and the German and British patents disclose latching mechanisms with over-center or similar preloaded latching action. Forg, Comber, Michelson, Cooper, Jewell, Andrews, Henrichs, Smith et al, Bernhard, the three Poe patents, Stammreich et al, Richter, and VanHulle at al disclose adjustable latching mechanisms.
The above patents and the prior art that is discussed and/or cited therein should be studied for the purpose of putting the present invention into proper perspective relative to the prior art.